Starting assembly for a carburetor

ABSTRACT

A starting device for a rotary throttle valve-type carburetor enables adjustment of the quantity of air and fuel delivered to an engine to facilitate the cold start of the engine. The starting device changes the position of the throttle valve prior to starting the engine to adjust the fuel and air mixture delivered to the engine as desired to facilitate starting and initial warming up of the engine.

REFERENCE TO RELATED APPLICATION

[0001] Applicants claim priority of Japanese patent applications, Ser.No. 2001-374,117, filed Dec. 7, 2001, Ser. No. 2001-374,118, filed Dec.7, 2001 and Ser. No. 2001-374,119.

FIELD OF THE INVENTION

[0002] The present invention relates to a rotary throttle valvecarburetor for an internal combustion engine, and more particularly tosuch a carburetor having a starting device.

BACKGROUND OF THE INVENTION

[0003] The conventional rotary throttle valve-type carburetor isdesigned so that turning of the throttle valve causes a needle to bemoved up and down to adjust the extent to which a fuel nozzle is open.In low temperatures when the engine is cold, frictional resistance inthe engine is high. Therefore, the engine is hard to start, and even ifthe engine is started its idle operation is unstable.

[0004] As shown in FIG. 51, a conventional rotary throttle valve-typecarburetor has a carburetor body 5 provided with a cylindrical valvechamber 6 perpendicular to an air intake passage (extending verticallyrelative to the paper surface) a throttle valve 1 having a throttle hole2 is rotatably and vertically moveably fitted in the valve chamber 6. Avalve shaft 1 a of the throttle valve 1 extends through a lid plate 21for closing the valve chamber 6, and a throttle valve lever 22 isconnected to the upper end of the valve shaft 1 a. A swivel 23 forconnecting a remote control cable is rotatably supported on one end ofthe throttle valve lever 22, whereas a cam portion 22 a is provided onthe other end of the throttle valve lever 22. A peripheral cam groovewith a depth that becomes gradually shallower in a direction of rotationcorresponding to an increased throttle valve opening is provided in thelower surface of the cam portion 22 a and a follower supported on thelid plate 21 is engaged with the cam groove to thereby constitute a cammechanism.

[0005] Fuel is taken into a fuel nozzle of a fuel supply pipe 4projecting toward the throttle hole 2 via a check valve and a fuel jet.In FIG. 51, the throttle valve 1 is in a fully open position, and thethrottle hole 2 and the air intake passage are substantially registeredor coincident in an axial direction. A needle 3 projecting downward fromthe throttle valve 1 is inserted into the fuel supply pipe 4.

[0006] In operation, to increase the speed and/or power of the engine,the throttle valve lever 22 is turned or rotated in an acceleratingdirection against the force of a spring to increase the extent to whichthe throttle hole 2 is open relative to the air intake passage. At thesame time, the needle 3 is moved up by the aforementioned cam mechanismto increase the extent to which the fuel nozzle is open.

[0007] A start shaft 32 is fitted into a guide tube 53 formed integralwith the lid plate 21, and when the start shaft 32 is turned by means ofa start lever 31, a cam surface 52 formed on the end portion of thestart shaft 32 lifts up the throttle lever 22 so as to increase thequantity of fuel. A pin 51 on the guide tube 53 is engaged with anannular groove of the start shaft 32 to retain the start shaft 32 in theguide tube 53.

[0008] In a small engine for a work tool provided with a centrifugalclutch and the aforementioned rotary throttle valve-type carburetor,when the airflow through the carburetor is increased sufficiently overthe calibrated air flow for idle engine operation (thereby increasingthe engine rpm at idle), the centrifugal clutch can become connected sothat a tool driven by the engine is actuated, which may be undesirable.Accordingly, the airflow when the engine is started has to be set sothat the speed (rpm) of the engine is slightly faster than thecalibrated idle setting, but not so high as to engage the clutch.

[0009] However, after the break-in period of the engine, the set idlespeed becomes faster than the value set after assembly at the factory.At this time, when the idling speed is adjusted to a proper value theincrease in airflow at the start of the engine as adjusted by the startfuel increasing mechanism, can place the speed of the engine out of itsdesired range.

SUMMARY OF THE INVENTION

[0010] A starting device for a rotary throttle valve-type carburetorenables adjustment of the quantity of air and fuel delivered to anengine to facilitate the cold start of the engine. In one embodiment,the starting device has an axially slidable sleeve fitted into a guidetube supported on a lid plate for closing a valve chamber of acarburetor body. A pin extending through the sleeve is engaged with anaxial slit of the guide tube. A first projecting part extends outwardlyfrom the guide tube and a second projecting part extends outwardly fromthe sleeve, and an idling adjusting bolt extends through the secondprojecting part and is threadedly fitted in the first projecting part. Astart shaft having a helical groove in engagement with the pin is fittedinto the sleeve, and has an actuator comprising at least in part a flatcam surface for engagement with a cam plate provided on a valve shaft ofa throttle valve. A push rod for engagement with a side wall surfaceprovided on the valve shaft is formed on the end of the start shaft.When the start shaft is rotated, the cam surface engages and lifts thethrottle valve to increase fuel flow, and the push rod rotates thethrottle valve to further open it and increase the air flow. Byadjusting the position of the cam surface and the push rod relative tothe throttle valve, the extent of the increase in fuel flow and air flowcan be adjusted to provide a desired fuel and air mixture to facilitatestarting the engine.

[0011] In another embodiment, a start shaft is threaded in a bossportion formed on the lid plate. A cam surface is formed on the endportion of the start shaft, a push rod is threaded in the start shaft,and a protrusion is formed on the lower surface of a throttle valvelever connected to a valve shaft of the throttle valve. When the startshaft is rotated, a throttle valve lever is lifted up by the camsurface, and the protrusion on the throttle valve lever is pushed by theaxial movement of said start shaft and push rod to turn or rotate thethrottle valve lever.

[0012] In another embodiment, the actuator comprises an eccentric pushrod with a cam surface to both lift and rotate the throttle valve lever.Several other embodiments of carburetors with starting assemblies aredisclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] These and other objects, features and advantages will be apparentfrom the following detailed description of the preferred embodiments,appended claims and accompanying drawings in which:

[0014]FIG. 1 is a side view of a rotary throttle valve-type carburetorprovided with a starting device according to a first embodiment of thepresent invention;

[0015]FIG. 2 is a plan view of the rotary throttle valve-typecarburetor;

[0016]FIG. 3 is a plan view showing, in an enlarged scale, a portion ofthe rotary throttle valve-type carburetor;

[0017]FIG. 4 is a front view showing a throttle valve lever and a cam ofthe rotary throttle valve-type carburetor;

[0018]FIG. 5 is an exploded plan view showing portions of the startingdevice of the rotary throttle valve-type carburetor;

[0019]FIG. 6 is a fragmentary front sectional view of a rotary throttlevalve-type carburetor provided with a starting device according to asecond embodiment of the present invention;

[0020]FIG. 7 is a partial plan sectional view of the rotary throttlevalve-type carburetor of FIG. 6;

[0021]FIG. 8 is a fragmentary side sectional view of the rotary throttlevalve-type carburetor of FIG. 6;

[0022]FIG. 9 is a plan view of a rotary throttle valve-type carburetorprovided with a starting device according to a third embodiment of thepresent invention;

[0023]FIG. 10 is a front view showing portions of the starting device ofthe rotary throttle valve-type carburetor of FIG. 9;

[0024]FIG. 11 is a plan view of a rotary throttle valve-type carburetorprovided with a starting device according to a fourth embodiment of thepresent invention;

[0025]FIG. 12 is a front view showing the starting device of the rotarythrottle valve-type carburetor of FIG. 11;

[0026]FIG. 13 is a side sectional view showing the rotary throttlevalve-type carburetor of FIG. 11;

[0027]FIG. 14 is a side sectional view showing the starting device ofthe rotary throttle valve-type system carburetor of FIG. 11;

[0028]FIG. 15 is a fragmentary plan sectional view showing the startingdevice of the rotary throttle valve-type carburetor of FIG. 11;

[0029]FIG. 16 is a fragmentary front sectional view showing the startingdevice of the rotary throttle valve-type carburetor of FIG. 11;

[0030]FIG. 17 is a fragmentary front sectional view showing the startingdevice of the rotary throttle valve-type carburetor of FIG. 11;

[0031]FIG. 18 is a fragmentary front sectional view showing the startingdevice of the rotary throttle valve-type carburetor of FIG. 11;

[0032]FIG. 19 is an exploded perspective view showing a part of thestarting device of the rotary throttle valve-type carburetor of FIG. 1;

[0033]FIG. 20 is a plan view of a rotary throttle valve-type carburetorprovided with a starting device according to a fifth embodiment of thepresent invention;

[0034]FIG. 21 is a front sectional view showing the starting device ofthe rotary throttle valve-type carburetor of FIG. 20;

[0035]FIG. 22 is a side sectional view showing the starting device ofthe rotary throttle valve-type carburetor of FIG. 20;

[0036]FIG. 23 is a side sectional view taken generally along line23A-23A of FIG. 21 showing the starting device of the rotary throttlevalve-type carburetor;

[0037]FIG. 24 is a fragmentary plan sectional view taken generally alongline 24A-24A of FIG. 22 showing the starting device of the rotarythrottle valve-type carburetor;

[0038]FIG. 25 is a fragmentary front sectional view taken generallyalong line 25A-25A of FIG. 22 showing the starting device of the rotarythrottle valve-type carburetor of FIG. 20;

[0039]FIG. 26 is a fragmentary front sectional view showing the startingdevice of the rotary throttle valve-type carburetor of FIG. 20;

[0040]FIG. 27 is a fragmentary front sectional view showing the startingdevice of the rotary throttle valve-type carburetor of FIG. 20;

[0041]FIG. 28 is an exploded perspective view showing a part of thestarting device of the rotary throttle valve-type carburetor of FIG. 20;

[0042]FIG. 29 is a fragmentary plan view of a rotary throttle valve-typecarburetor provided with a starting device according to a sixthembodiment of the present invention;

[0043]FIG. 30 is a fragmentary front view showing the starting device ofthe rotary throttle valve-type carburetor of FIG. 29;

[0044]FIG. 31 is a fragmentary front view showing the starting device ofthe rotary throttle valve-type carburetor of FIG. 29;

[0045]FIG. 32 is a plan view of a rotary throttle valve-type carburetorprovided with a starting device according to a seventh embodiment of thepresent invention;

[0046]FIG. 33 is a front view showing the starting device of the rotarythrottle valve-type carburetor of FIG. 32;

[0047]FIG. 34 is a side view showing the starting device of the rotarythrottle valve-type carburetor of FIG. 32;

[0048]FIG. 35 is a fragmentary side sectional view showing the startingdevice of the rotary throttle valve-type carburetor of FIG. 32;

[0049]FIG. 36 is a plan sectional view taken generally along line36A-36A in FIG. 34 showing the starting device of the rotary throttlevalve-type carburetor;

[0050]FIG. 37 is a fragmentary front sectional view showing the startingdevice of the rotary throttle valve-type carburetor of FIG. 32;

[0051]FIG. 38 is a fragmentary side sectional view taken generally alongline 38A-38A in FIG. 37 showing the starting device of the rotarythrottle valve-type carburetor;

[0052]FIG. 39 is a fragmentary front sectional view showing the startingdevice of the rotary throttle valve-type carburetor of FIG. 32.

[0053]FIG. 40 is a front sectional view of a rotary throttle valve-typecarburetor provided with a starting device according to an eighthembodiment of the present invention;

[0054]FIG. 41 is a plan view showing the starting device of the rotarythrottle valve-type carburetor of FIG. 40;

[0055]FIG. 42 is a side sectional view showing a part of the startingdevice of the rotary throttle valve-type carburetor of FIG. 40;

[0056]FIG. 43 is a side sectional view showing a part of the startingdevice of the rotary throttle valve-type carburetor of FIG. 40;

[0057]FIG. 44 is a front sectional view of a rotary throttle valve-typecarburetor provided with a starting device according to a ninthembodiment of the present invention;

[0058]FIG. 45 is a plan view showing a part of the starting device ofthe rotary throttle valve-type carburetor of FIG. 44;

[0059]FIG. 46 is a front sectional view of a rotary throttle valve-typecarburetor provided with a starting device according to a tenthembodiment of the present invention;

[0060]FIG. 47 is a fragmentary sectional view taken generally along line47A-47A of FIG. 46 showing a lid plate of the starting device of therotary throttle valve-type carburetor;

[0061]FIG. 48 is a perspective partial sectional view showing a part ofthe starting device of the rotary throttle valve-type carburetor of FIG.46;

[0062]FIG. 49 is a fragmentary side sectional view showing a part of thestarting device of the rotary throttle valve-type carburetor of FIG. 46;

[0063]FIG. 50 is a fragmentary side sectional view showing a part of thestarting device of the rotary throttle valve-type carburetor of FIG. 46;

[0064]FIG. 51 is a front sectional view of a conventional rotarythrottle valve-type carburetor according to the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] As shown in FIGS. 1 and 2, in the rotary throttle valve-typecarburetor an air cleaner and a heat insulating pipe are butted on thefront and rear end flanges 5 a and 5 b of a carburetor body 5 throughwhich an air intake passage extends longitudinally. The body isconnected to the engine by a pair of mounting bolts. An intermediateplate 10 defining in part a fuel pump is connected to the lower surfaceof the carburetor body 5 through a fuel pump diaphragm 9. Anotherintermediate plate 13 defining in part a fuel metering chamber isconnected to the lower surface of the intermediate plate 10 through afuel metering diaphragm 12. A primer and purge assembly 18 has a bulb 17connected to the lower surface of the intermediate plate 13 by means ofa keep plate 15. Fuel in a fuel tank is supplied to the fuel meteringchamber via a fuel inlet pipe 25 and a fuel pump. When the primer andpurge assembly 18 is operated by depressing the bulb 17 repeatedly, fuelvapor or the like in the fuel metering chamber is returned to the fueltank via a return pipe 19 and liquid fuel is drawn into fuel passagesand chambers in the carburetor.

[0066] The fuel pump may be of generally conventional construction, suchas that shown in the prior art carburetor of FIG. 51. When pulsatingpressure of a crankcase chamber of the engine is introduced into achamber defined by the fuel pump diaphragm 9, the diaphragm 9 isdisplaced so that fuel in a fuel tank, not shown, is taken into a lowerchamber or a pump chamber defined by the diaphragm 9 via the fuel inletpipe 25, a filter and a pump inlet valve, and is further discharged intoa fuel metering chamber 20 on the upper side of the diaphragm 12 througha pump outlet valve and an inlet valve 28 of a fuel metering assembly.

[0067] The fuel metering assembly may also be of generally conventionalconstruction as shown in FIG. 51. This assembly has a lever 26 supportedin the fuel metering chamber 20 by means of a shaft 27, one end of thelever is biased and engaged with a center protrusion of the diaphragm 12by the force of a spring, and the other end of the lever is engaged withthe lower end of the inlet valve 28. Fuel enters the fuel meteringchamber 20 through the inlet valve 28 which opens and closes in responseto displacement of the diaphragm 12. The chamber on the side of thediaphragm 12 opposite the fuel metering chamber 20 is open to theatmosphere. Fuel in the fuel metering chamber 20 is taken into the fuelsupply pipe 4 which has an opening or nozzle projecting toward thethrottle hole 2 via a check valve and a fuel jet.

[0068] Returning to FIGS. 1 and 2, a lid plate 21 is put on the uppersurface of the carburetor body 5 and secured by means of bolts 24. Athrottle valve lever 22 having an arcuate cam portion 22 a is connectedto the upper end of a valve shaft 1 a of the throttle valve projectedupward through the lid plate 21. A swivel 23 for connecting aremote-control cable is supported on the throttle valve lever 22, andthe throttle valve lever 22 is normally brought into contact with anidling adjusting bolt 26 by the force of a return spring (not shown).

[0069] An axial slit 34 is provided on the upper wall of a guide tube 35which is connected to the lid plate 21 or formed integrally with the lidplate 21, and a tapped hole for threadedly receiving the idlingadjusting bolt 26 is provided in a projection 35 a extending outwardlyfrom the guide tube 35. A sleeve 33 is fitted into the guide tube 35,and a pin 33 a extending through the peripheral wall of the sleeve 33 isengaged with a shoulder defined by the slit 34. The idling adjustingbolt 26 extends through a flange 33 b of the sleeve 33 and a spring 26 aand is threadedly engaged with the projection 35 a. The throttle valvelever 22 is brought into contact with the end of the idling adjustingbolt 26 by the force of a return spring to control an idling position ofthe throttle valve lever 22.

[0070] As shown in FIGS. 3-5, a start shaft 38 provided with a startlever 31 is fitted into the sleeve 33. An actuator is associated withthe start shaft, and as shown here, comprises a cam 38 a having a flatcam surface 38 b provided on an end portion of the start shaft 38, and apush rod 40 provided on the shaft center of the end of the start shaft38. Further, the start shaft 38 is provided with a helical groove 39(FIG. 5) in engagement with the pin 33 a projecting into the sleeve 33.

[0071] As mentioned above, the sleeve 33 is fitted into the immovableguide tube 35, and the start shaft 38 is fitted into the sleeve 33 sothat the helical groove 39 engages the pin 33 a of the sleeve 33. Oneend of a spring 43 wound about the distal end of the start shaft 38 isengaged at a groove 43 a (FIG. 5) of the sleeve 33, while the other endof the spring 43 is stopped on the start lever 31. The start lever 31 isnormally biased to a first position by the force of the spring 43. Inthis position, as shown in FIG. 4, a clearance is formed between the cam38 a and the lower surface of the throttle valve lever 22. As shown inFIG. 3, a cam plate 42 is provided on the valve shaft 1 a of thethrottle valve 1, especially between the throttle valve lever 22 and thecam portion 22 a, and a flat side wall surface 44 is provided below thecam plate 42.

[0072] When the start lever 31 is turned to its second position toprepare for a cold start of the engine, the flat cam surface 38 bengages the lower surface of the cam plate 42 to lift up the throttlevalve lever 22. Correspondingly, this movement of the throttle valveincreases the extent to which the fuel nozzle is open or stateddifferently, the flow area of the nozzle is increased. This enables aricher than normal fuel and air mixture to be delivered to the engine tofacilitate starting it.

[0073] Simultaneously, the start shaft 38 is moved in an axial direction(in the direction of the arrow y in FIG. 5) by the engagement betweenthe helical groove 39 of the start shaft 38 and the pin 33 a. The axialmovement of the start shaft 38 causes the push rod 40 to engage anddisplace the side wall surface 44 of the valve shaft 1 a which rotatesthe throttle valve lever 22. This in turn increases the effective flowarea through the throttle hole of the throttle valve. In this manner,upward movement and rotation of the throttle valve 1 are achieved by therotation of the start lever 31, so the quantity of fuel and airdelivered to the engine increases to obtain smooth starting and initialidle operation of the engine.

[0074] After warming up the engine, the throttle valve lever 22 isturned to further open the throttle valve, and the throttle valve lever22 is lifted up by the normal cam mechanism and moved away from the camsurface 38 b. Therefore, the start shaft 38 having the cam 38 a isreturned to its first position by the force of the spring 43 preventingfurther interaction with the throttle valve to permit normal carburetoroperation.

[0075] As just described, the cam surface 38 b and the push rod 40 areprovided on the start shaft 38 which is turned by the start lever 31.The cam surface 38 b can be engaged with the cam plate 42 formedintegral with the valve shaft 1 a and the push rod 40 can be engagedwith the side wall surface 44 formed integral with the valve shaft 1 a.Therefore, the distance and location from the start shaft center of thecam surface 38 b and the axial dimension or effective length of the pushrod 40 are adapted to the desired starting characteristics of the engineto thereby provide a desired fuel and air mixture to the engine tofacilitate starting and warming up the engine. Since the fuel quantityand the air quantity can be adjusted separately, machining is easilyaccomplished.

[0076] In case the engine idle speed is adjusted according to theoperating hysteresis or operating environment of the engine by, forexample, retracting the idling adjusting bolt 26, the throttle valvelever 22 is positioned at idle further away from its wide open positionto reduce the air flow at idle. The sleeve 33 and the start shaft 38 aremoved back in the axial direction at the same time, and therefore, therelative spacing between the push rod 40 of the start shaft 38 and theside wall surface 44 of the valve shaft 1 a remains unchanged. Theincreased quantity of fuel and air when the start lever 31 is rotated toits second position before the cold start of the engine is almost thesame as the case prior to the adjustment of the idle position of thethrottle valve. Since the airflow at idle is reduced by retracting theidling adjusting bolt 26, the air/fuel ratio becomes more rich since theincreased fuel flow can remain essentially the same as before adjustmentof the idling adjustment bolt 26.

[0077] Second Embodiment

[0078] In the embodiment shown in FIGS. 6 to 8, the lid plate 21 forclosing the valve chamber is fixed on the carburetor body 5 by aplurality of bolts 24, and the throttle valve lever 22 is connected tothe upper end of the valve shaft 1 a extending through the lid plate 21.As shown in FIG. 8, the valve shaft 1 a is covered with a dust-proofboot 1 b. The swivel 23 is supported on the end of the throttle valvelever 22, a cam portion 22 a is formed integral with the other endthereof. A cam groove in engagement with a follower 54 projecting fromthe lid plate 21 is provided in the cam portion 22 a, as shown in FIGS.6 and 7. A projecting wall 22 b is projected downward from the lowersurface 22 c of the throttle valve lever 22. The idling adjusting bolt26 is threadedly fitted in a projecting wall 21 a which is projectedupward from a side edge of the lid plate 21. A boss portion or a guidetube 21 b is formed integral with the lid plate 21, especially adjacentto the projecting wall 21 a, and a start shaft 58 having a start lever59 and an actuator associated therewith is rotatably fitted into theguide tube 21 b. A helical or arcuate groove 57 is formed in the outerperipheral surface of the start shaft 58, and a guide pin 56 inengagement with the helical groove 57 is secured to the guide tube 21 b.The actuator comprises, at least in part, the push rod 55 and a camsurface 58 a. The push rod 55 is threadedly fitted in a tapped hole 60provided in the shaft center of the start shaft 58, and the extreme endof the push rod 55 can be placed in contact with the projecting wall 22b. The flat cam surface 58 a is formed on the end portion of the startshaft 58 to be engagable with the lower surface 22 c of the throttlevalve lever 22.

[0079] The start lever 59 is normally in a first position wherein thecam surface 58 a is moved away from the lower surface 22 c of thethrottle valve lever 22, and the push rod 55 is close to the projectingwall 22 b but is not in contact therewith. When the start lever 59 isrotated toward its second position in preparation for starting a coldengine, the start shaft 58 is moved generally axially as while guided bythe engagement of the guide pin 56 and groove 57. At this time, as shownin FIGS. 6 and 8, the cam surface 58 a comes in contact with the lowersurface 22 c of the throttle valve lever 22 to lift up the throttlevalve lever 22. At the same time, the push rod 55 impinges on theprojecting wall 22 b (as shown in FIGS. 6 and 7) to rotate the throttlevalve lever 22 toward its wide open position.

[0080] As described above, when the throttle valve lever 22 is moved upby the cam surface 58 a, the extent to which the fuel nozzle of the fuelsupply pipe is open increases to increase the quantity of fuel deliveredto the engine. At the same time, when the throttle valve lever 22 isrotated by the push rod 55, the extent to which the throttle hole of thethrottle valve is open increases to increase the quantity of air. Theamount that the throttle valve lever 22 is lifted is determined by thedistance from the center of the start shaft 58 to the cam surface 58 a.The amount the throttle valve lever 22 is rotated can be adjusted byadvancing or retracting the push rod 55 in the tapped hole 60 of thestart shaft 58. Accordingly, both the fuel flow and the air flow at thecold start of the engine can be adjusted independently to provideimproved starting and more stable idle engine operation after startingthe engine. It is also possible to avoid increasing the engine idlingspeed which may be desirable to avoid engagement of a centrifugal clutchif one is used with the engine.

[0081] Third Embodiment

[0082] In the embodiment shown in FIGS. 9 and 10, a lid plate 121 is puton the upper surface of the carburetor body 105 and secured thereto bymeans of bolts 124. A throttle valve lever 122 having a quadrant-shapedcam 122 a is connected to the upper end of a valve shaft 101 a of athrottle valve, the valve shaft 101 a extending upwardly through the lidplate 121. The throttle valve lever 122 is normally placed in contactwith an idling adjusting bolt 126 by the force of a return spring, notshown. The throttle valve lever 122 is provided with a cam plate 142 andan outwardly extending projection 142 a is formed on the outer edge ofthe cam plate 142.

[0083] A start shaft 143 is fitted into an axial hole 135 b of a guidetube 135 which is connected to the lid plate 121 or formed integral withthe lid plate 121. A pin 151 mounted on the guide tube 135 is engagedwith an annular groove formed on the start shaft 143. An idlingadjusting bolt 126 having a locking spring 126 a wound thereabout isthreadedly fitted through a flange 135 a projected outwardly from theguide tube 135.

[0084] An actuator associated with the start shaft 143 comprises, atleast in part, a push rod 138 b and a cam 138. The cam 138 is formed onthe end portion of the start shaft 143 and a flat cam surface 138 a isformed on the outer peripheral surface of the cam 138. The push rod 138b extends outwardly from the cam surface 138 a.

[0085] One end of a spring 143 a wound about the distal end portion ofthe start shaft 143 is fastened on the guide tube 135 and the other endof the spring 143 a is fastened on a start lever 131. The start lever131 is normally biased to its first position by the force of the spring143 a. At this time, as shown in FIG. 10, there is a clearance gapbetween the cam 138 and the lower surface of the cam plate 142.

[0086] Before a cold start of the engine, the start lever 131 is rotatedtoward its second position so that the cam surface 138 a of the startshaft 143 engages the lower surface of the cam plate 142 to lift up thethrottle valve lever 122, thus increasing the extent to which the fuelnozzle is open. At the same time, the rod 138 b of the start shaft 143pushes the projection 142 a on the outer edge of the cam plate 142 torotate the throttle valve lever 122, thus increasing the extent to whichthe throttle valve is open. In this manner, upward movement and rotationof the throttle valve are achieved by the rotation of the start shaft143. Therefore, the air flow increases simultaneously with the increaseof the fuel flow to obtain a smooth start and initial idle operation ofthe engine.

[0087] After idling of the engine, when the throttle valve lever 122 isrotated towards its fully open position, the throttle valve lever 122 islifted up by the normal cam mechanism and moved away from the camsurface 138 a, whereby the start shaft 143 is returned to its firstposition by the force of the spring 143 a. In its first position, thestart shaft and related components do not engage or interfere with thethrottle valve movement.

[0088] In this embodiment, the cam surface 138 a and the push rod 138 bare provided on the start shaft 143. The cam surface 138 a can beengaged with the cam plate 142 integral with the throttle valve lever122, and the push rod 138 b can be engaged with the projection 142 a ofthe cam plate 142. Therefore, the height of the cam surface 138 a fromthe start shaft center and the position and length of the push rod 138 bcan be adjusted or altered to adapt to the starting characteristics ofthe engine. Additionally, the increase in fuel flow and the increase inair flow can be separately adjusted.

[0089] Fourth Embodiment

[0090] Another embodiment carburetor is shown in FIGS. 11 to 19. Asshown in FIGS. 11 and 12, the rotary throttle valve-type carburetorprovided with a starting device has a carburetor body 220 made ofaluminum and provided with an air intake passage 218 extendingtherethrough and a pair of left and right through-holes 212 provided onfront and rear end flanges of the carburetor body 220, respectively. Anair cleaner is connected on the front end flange in FIG. 11, and therear end flange is connected through a heat insulating pipe to the wallsurrounding an intake port of the engine by a pair of bolts extendingthrough the through-holes 212. A throttle valve 219 having a throttlehole is rotatably and vertically moveably fitted into a cylindricalvalve chamber perpendicular to the air intake passage 218. A valve shaft206 extends from the upper end of the throttle valve 219, through a lidplate 202 that is preferably formed of synthetic resin, for closing thevalve chamber. A throttle valve lever 207 is mounted on the upper end ofthe valve shaft 206. A swivel 207 a for fastening an inner cable of aremote control cable is supported on one end of the throttle valve lever207. An arcuate cam 207 b extends outwardly from the throttle valvelever 207. A cam groove of varied depth is provided in the lower surfaceof the cam 207 b, and a follower (not shown) supported on the lid plate202 is engaged with the cam groove to constitute a cam mechanism.

[0091] The lid plate 202 has an inverted L-shape in FIG. 11, and is puton the upper face of the carburetor body 220 together with a reinforcingplate 203 made of metal having a ledge 203 a and fastened to thecarburetor body 220 by a pair of bolts 204. Mounting metal fittings (notshown) for supporting an end of an outer tube of the remote controlcable is threadedly supported on an upstanding wall 203 b of thereinforcing plate 203. An inner wire inserted into the outer tube isextended over a guide wall 205 of the lid plate 202 and fastened to theswivel 207 a.

[0092] An upstanding projection 202 a is formed integral with the lidplate 202, an idling adjusting bolt 215 is threadedly fitted in theupper portion of the projection 202 a, and a pushing shaft 227threadedly receives a push rod 217 and is un-rotatably and axiallymovably supported at the lower portion of the projecting wall 202 a.Further, a start shaft 230 (FIGS. 13-15) provided with a start lever 210is rotatably fitted into a cylindrical portion in the projection 202 a,as shown in FIGS. 13 and 14. As shown in FIGS. 11 and 19, a pin 209 asupported on the projection 202 a is engaged with an annular groove 209b provided on the start shaft 230. A helical or arcuate projection 233is partially formed integral with the start shaft 230, and a projectingpiece having a groove 227 a for engagement with the helical projection233 is provided on the pushing shaft 227. Flat cam surfaces 234 and 234a are formed on the end portion of the start shaft 230. When the startlever 210 is in its first position as shown in FIG. 13, the cam surface234 does not contact the lower side of a cam plate 208 (FIG. 11) formedintegral with the throttle valve lever 207. The push rod 217 and camsurface 234 comprise at least part of an actuator associated with thestart shaft.

[0093] As shown in FIGS. 12 and 16, a coil spring 231 is wound about thestart shaft 230, and one end of the coil spring 231 is stopped at theprojection 202 a and the other end of the coil spring 231 is stopped atthe start lever 210. The start lever 210 is rotated and biased to itsfirst position, shown in FIGS. 13 and 16, by the force of the coilspring 231. A downwardly projecting edge 240 is formed integral with thethrottle valve lever 207, an end of the idling adjusting bolt 215 isengaged with the edge 240, and an end of the push rod 217 threadedlyfitted in the pushing shaft 227 is arranged to be able to engage withthe edge 240. However, normally, the push rod 217 is not in contact withthe edge 240.

[0094] At the time of cold start of the engine, when the start lever 210is moved to its second position as shown in FIG. 18, the pushing shaft227 in which the helical projection 233 and the groove 227 a are engagedis advanced forward (to the left as viewed in FIG. 18) and the push rod217 impinges upon the edge 240 to rotate the throttle valve lever 207toward its fully open position. At the same time, the start shaft 230 isrotated to engage the cam surface 234 a with a cam plate 208 integralwith the throttle valve lever 207. By doing so, the throttle valve 219is lifted up together with the throttle valve lever 207 by the camsurface 234 a on the start shaft 230.

[0095] In this manner, the degree or amount to which the throttle valve219 and the fuel nozzle are open increases, whereby a rich mixture issupplied to the engine during cranking of the engine and a smooth startof the engine is obtained. Also, since the air quantity increasesslightly at the starting of the engine, the initial idling operationafter the start is smoother and stable. The amount of upward movement orlift of the throttle valve lever 207 is determined according to thedistance from the center of the start shaft 230 to the cam surface 234a. Further, the amount that the throttle valve lever 207 is rotated whenthe edge 240 is pushed by the push rod 217 is adjusted by retracting oradvancing the push rod 217 with respect to the pushing shaft 227.

[0096] After the engine has been warmed up, when the throttle valve 207is rotated toward its fully open position, the cam plate 208 rotatestogether with the throttle valve lever 207 and is disengaged from thecam surface 234 a. At this time, the start lever 210 is returned to itsfirst position by the force of the coil spring 231. At the same time,the pushing shaft 227, having the projecting piece with the groove 227 aengaged with the helical projection 233 of the start shaft 230, isretracted to its first position.

[0097] Fifth Embodiment

[0098] In the embodiments shown in FIGS. 20 to 28, a push rod 217 forrotating the throttle valve lever 207 is threadedly supported on a startshaft 237, and a gear 222 (FIGS. 23 and 28) on the cam shaft 237 ismeshed with a gear 221 (see FIG. 28) which is provided on a start shaft230 a for lifting up the throttle valve lever 207. The idling adjustingbolt 215 is threadedly fitted in the upper portion of the projection 202a formed on the right side edge of the lid plate 202, and the startshaft 237 is rotatably and axially movably supported on the cylindricalportion on the lower portion of the projection 202 a. Further, the camshaft 230 a is rotatably and axially un-movably fitted into thecylindrical portion of the projection 202 a. Therefore, a pin 209 asupported on the projection 202 a is engaged with a groove 209 bprovided on the cam shaft 230 a, as shown in FIGS. 20 and 28. Thepartial gear 221 is formed integral with the distal end of the cam shaft230 a. The flat cam surfaces 234 and 234 a are formed on the end portionof the cam shaft 230 a. When the start lever 210 is in its firstposition the cam surface 234 is adjacent to but not contacting the lowersurface of the cam plate 208 (FIG. 20) formed integral with the throttlevalve lever 207.

[0099] As shown in FIGS. 24 and 25, the coil spring 231 is wound aboutthe start shaft 237, and one end of the coil spring 231 is stopped atthe projection 202 a and the other end of the coil spring 231 is stoppedat the start lever 210. The start lever 210 is rotated and biased to itsfirst position, shown in FIG. 25, by the force of the coil spring 231.The edge 240 projecting downward is formed integral with the side edgeof the throttle valve lever 207, the extreme end of the idling adjustingbolt 215 comes in contact with the edge 240. The push rod 217 which isthreadedly fitted in a tapped hole 223 of the start shaft 237 isarranged so that its end is engagable with the edge 240 during at leasta portion of the movement of the start shaft 237. However, the push rod217 is normally not in contact with the edge 240. The push rod 217 andcam surface 234 comprise at least part of an actuator associated withthe start shaft.

[0100] When a cold engine is going to be started, the start lever 210 isrotated to its second position, as generally shown in FIG. 27. Therotation of the start lever 210 causes the start shaft 237 to begenerally axially advanced as guided by a pin 229 a in the groove 229 b,and the push rod 217 impinges upon the edge 240 to rotate the throttlevalve lever 207 toward its fully open position. At the same time, thecam shaft 230 a having the gear 221 meshed with the gear 222, isrotated. The cam surface 234 a engages the cam plate 208 on the throttlevalve lever 207, and the throttle valve 219 is lifted up together withthe throttle valve lever 207. In this manner, the amount to which thethrottle valve 219 and fuel nozzle are open increases, whereby a richmixture is supplied to the engine upon cranking of the engine tofacilitate starting and initial idle operation as the engine is warmedup. The amount of upward movement (lift) of the throttle valve lever 207is determined according to the distance from the center of the cam shaft230 a to the cam surface 234 a. Further, the amount that the throttlevalve lever 207 is rotated when the edge 240 is pushed by the push rod217 is adjusted by retracting or advancing the push rod 217 with respectto the start shaft 237.

[0101] After the engine has been warmed up, when the throttle valvelever 207 is rotated toward its fully open position, the cam plate 208is rotated together with the throttle valve lever 207 and is disengagedfrom the cam surface 234 a. At this time, the start lever 210 isreturned to its first position by the force of the coil spring 231. Thecam shaft 230 a having the gear 221 meshed with the gear 222 of thestart shaft 237 is also returned to its first position.

[0102] Sixth Embodiment

[0103] In the embodiments shown in FIGS. 29 to 31, when a cam surface241 formed in a side edge of a throttle valve lever 207 comes in contactwith a push rod 217 serving as an idling adjusting bolt to rotate astart shaft 230 and lift up the throttle valve lever 207, a cam surface241 is pushed so that the throttle valve lever 207 is slightly rotatedtoward its wide open position. The push rod 217 and a cam surface 234define at least part of an actuator associated with the start shaft. Thestart shaft 230 having a start lever 210 is rotatably and axiallyun-movably supported on the cylindrical portion of the projection 202 aon the lid plate 202. In order to accomplish this, a pin 209 a supportedon the projecting wall 202 a is engaged with an annular groove (as inthe embodiment of FIG. 19) provided on the peripheral surface of thestart shaft 230. Cam surfaces 234 and 234 a are formed on the end of thestart shaft 230 and positioned below the cam plate 208 formed integralwith the throttle valve lever 207. One end of the coil spring 231 woundabout the start shaft 230 is stopped on the projection 202 a and theother end of the coil spring 231 is stopped at the start lever 210,similar to the embodiment of FIG. 12. A push rod 217 serving as anidling adjusting bolt threadedly supported on the projection 202 a hasits end engaged with the cam surface 241 formed on the side edge of thethrottle valve lever 207 and is biased by a return spring (not shown)that returns the throttle valve to an idling position. The cam surface241 is formed into an inclined surface which becomes higher (projectstoward the push rod 217) gradually from the upper portion to the lowerportion of the throttle valve lever 207.

[0104] In its first position shown in FIGS. 29 and 30, the end of thepush rod 217 is engaged with the upper portion of the cam surface 241 tocontrol the normal idling position of the throttle valve lever 207 andhence, the throttle valve 219. When a cold engine is to be started, thestart lever 210 is rotated to its second position so that the camsurface 234 engages the cam plate 208 to lift the throttle valve lever207. At the same time, the lower portion of the cam surface 241 isengaged by the end of the push rod 217, and the throttle valve lever 207is rotated toward its fully open position. Due to an increase in fuelquantity caused by upward movement of the throttle valve lever 207 (andhence an increase in the flow area of the fuel nozzle), and an increasein air quantity caused by rotation of the throttle valve lever 207, arich fuel and air mixture is supplied to the engine to facilitatestarting the engine. In a portable work machine in which rotation of thecrank shaft of the engine is transmitted to a work tool through acentrifugal clutch, the air quantity at the time of cold start of theengine can be adjusted by the position of the push rod 217 relative tothe projecting wall 202 a, and this can be done independently of theadjustment of the fuel quantity so that the work tool is not rotated assoon as the engine is started.

[0105] Seventh Embodiment

[0106] As shown in FIGS. 32 to 34, a carburetor body 321 through whichan air intake passage 323 extends is connected to a wall surrounding anintake port of the engine by bolts inserted into left and rightthrough-holes 322 and typically through a heat insulating pipe. Avertical cylindrical valve chamber crossing the air intake passage 323is provided in the carburetor body 321, and a throttle valve having athrottle hole is rotatably and vertically movably fitted into the valvechamber. The valve chamber is closed by a lid plate 302 preferablyformed of synthetic resin and fastened together with an L-shaped metalreinforcing plate 303 by a plurality of bolts 305. A valve shaft 307formed integral with the throttle valve has a throttle valve lever 309connected to the upper end extending through the lid plate 302. A swivel308 is rotatably supported on one end of the throttle valve lever 309,and a cam portion 306 is formed on the other end of the throttle valvelever 309.

[0107] An upright wall 303 a is formed preferably by upwardly bendingthe left edge of a reinforcing plate 303 having a projection 303 b. Anend of an outer tube of a remote control cable is secured to the wall303 a by metal fittings, not shown. An inner wire inserted into theouter tube extends over a guide projecting wall 304 formed integral withthe lid plate 302 and is connected to the swivel 308. An idlingadjusting bolt 310 is threadedly supported on the projection 302 a thatextends upward from the right edge of the lid plate 302, and thethrottle valve lever 309 is placed in contact with the idling adjustingbolt 310, as shown in FIG. 32, by the force of a return spring (notshown).

[0108] For increasing the quantity of fuel and air delivered to theengine at the time of a cold start of the engine, a cylindrical bossportion 302 b is formed adjacent to the projection 302 a, and a startshaft 316 having a start lever 313 is fitted into the boss portion 302b. As shown in FIG. 35, a helical or arcuate groove 315 is formed on thestart shaft 316, and a pin 314 received in the groove 315 is secured tothe boss portion 302 b. As shown in FIG. 36, a push rod 319 isthreadedly fitted in a tapped hole 318 provided eccentrically in thestart shaft 316. The push rod 319 has a cam surface 320 on theperipheral surface of the free end of the push rod. An arcuateprojection 309 a extends downwardly from a lower surface 309 b of thethrottle valve lever 309 and is faced toward the end of the push rod319. The push rod 319 and cam surface 320 define at least in part anactuator associated with the start shaft.

[0109] As shown in FIGS. 36 and 37, when the start lever 313 is in itsfirst position, the push rod 319 does not contact the lower surface 309b of the throttle valve lever 309 or the projection 309 a. When it isdesired to start a cold engine, the start lever 313 and start shaft 316are rotated to their second position (shown in FIGS. 38 and 39), thepush rod 319 supported on the start shaft 316 moves upward to engage thecam 320 with the lower surface 309 b to lift up the throttle valvetogether with the throttle valve lever 309. Lifting the throttle valveincreases the flow area of the fuel nozzle. At the same time, the startshaft 316, having the groove 315 in engagement with the pin 314, isadvanced. The projection 309 a is pushed leftward (as viewed in FIG. 39)by the push rod 319 of the start shaft 316, and the throttle valve lever309 rotates slightly toward its wide open position permitting increasedair flow through the hole in the throttle valve shaft. In this manner,an increase in the amount of fuel and air are achieved to facilitate thesmooth start of the engine. The amount that the throttle valve lever 309is lifted can be adjusted by replacing the push rod 319 threadedlyfitted in the tapped hole 318 with one different in outside diameter atits end, or by changing the eccentricity of the tapped hole 318 tochange the position of the cam surface 320. Further, the amount that thethrottle valve lever 309 is rotated can be adjusted by advancing orretracting the push rod 319 in the tapped hole 318.

[0110] When the throttle valve lever 309 is rotated towards the wide orfully open throttle position after the start of the engine, the push rodbecomes disengaged from the throttle valve lever 309 and the operatinglever 313 is returned to its first position by the force of a coilspring (not shown) wound about the start shaft 316 and having one endstopped at the boss portion 302 b and the other end stopped at theoperating lever 313.

[0111] Eighth Embodiment

[0112]FIG. 40 is a front sectional view of a rotary throttle valve-typecarburetor provided with a start fuel increasing mechanism according toone embodiment of the present invention. FIG. 41 is a plan view of thecarburetor showing a throttle valve lever. The rotary throttlevalve-type carburetor provides a rear end flange 438 a on a carburetormain body 438. The flange 438 a is placed in contact with an intake portof the engine through a heat insulating pipe, not shown, and is securedto the wall of the engine by means of a pair of bolts extending throughleft and right through holes 438 b. The carburetor body 438 is providedwith a start fuel increasing mechanism A, a throttle valve lever 421, afuel metering supply mechanism B, and a purge-primer pump C. Thecarburetor main body 438 is provided with a cylindrical air intakepassage 417 longitudinally extending perpendicular to the paper surfaceand a cylindrical valve chamber 403 perpendicular to the air intakepassage 417. The valve chamber 403 has a throttle valve 405 rotatablyand vertically movably (axially moveably) inserted. The throttle valve405 is provided with a laterally extending throttle hole 405 b, and avalve shaft 405 a upwardly extending through a lid plate 434 for closingthe valve chamber 403 and has a throttle valve lever 421 connected tothe upper end of the valve shaft 405 a.

[0113] A spring 402 surrounding the valve shaft 405 a is interposedbetween the lid plate 434 and the throttle valve 405, and has one endstopped at the lid plate 434 and the other end stopped at the throttlevalve 405, respectively. An upper end portion of a needle 416 isthreadedly fitted in the hollow valve shaft 405 a, which is closed by acap 418. A jet 406 and a fuel supply pipe 404 are fitted and secured tothe bottom wall of the valve chamber 403. The fuel supply pipe 404receives the free end of the needle 416 for reciprocation to adjust theflow area of an opening of a fuel nozzle 404 a as a function of thevertical movement of the throttle valve 405. In the illustratedembodiment, a columnar support 438 c is projected from the bottom wallof the valve chamber 403 to the throttle hole 405 b in order to receiveat least in part the fuel supply pipe 404. The throttle valve shaft 405a has an opening 470 through its lower end and extending into thethrottle hole 405 b to receive the support 438 c and fuel supply pipe404.

[0114] In the fuel metering supply mechanism B, an intermediate plate423 is connected to the lower end of the carburetor main body 438 with afuel pump diaphragm 425 sandwiched therebetween. A pulsation pressurechamber 424 for introducing pulsation pressure of a crank chamber of a2-stroke engine is defined on the upper side of the diaphragm 425, and apump chamber is defined on the lower side of the diaphragm 425. An endplate fuel metering 430 is connected to the intermediate plate 423 witha fuel metering diaphragm 412 sandwiched therebetween. A fuel meteringchamber 413 is defined on the upper side of the diaphragm 412 and anatmospheric chamber 411 is defined on the lower side of the diaphragm412. A lever 408 rotatably supported on the wall of the fuel meteringchamber 413 has one end placed in contact with a projecting piece 412 aon the center portion of the diaphragm 412 by the force of a spring 409interposed between the lever 408 and the top wall of the fuel meteringchamber 413, and has the other end connected to an inlet valve 407.

[0115] When the diaphragm 425 is vibrated or displaced vertically bycrankcase pulsation pressure in the pulsation pressure chamber 424, fuelin a fuel tank (not shown) is drawn into the pump chamber 426 via a pipe439, a filter 437 and an inlet valve (not shown). Fuel in the pumpchamber 426 is discharged into the fuel metering chamber 413 via anoutlet valve (not shown), a chamber 436 of the carburetor body 438 andthe inlet valve 407. When the fuel metering chamber 413 is filled withfuel, the diaphragm 412 is pushed down and the inlet valve 407 is closedwith counterclockwise rotation of the lever 408 (as viewed in FIG. 40).Conversely, when fuel in the fuel metering chamber 413 is reduced, thediaphragm 412 is lifted up by intake vacuum pressure in the fuelmetering chamber 413 and atmospheric pressure in the atmospheric chamber411, and the inlet valve 407 opens with clockwise rotation of the lever408 against the force of the spring 409. Fuel in the fuel meteringchamber 413 is drawn into the throttle hole 405 b via a check valve 427preferably made of a thin elastic circular plate, the jet 406, the fuelsupply pipe 404 and the fuel nozzle 404 a, and is supplied to the enginewhile mixing with air flowing through the air intake passage 417.

[0116] In the purge-primer pump C for purging air and fuel vapor fromthe carburetor and replenishing fuel to the fuel metering chamber 413before the start of the engine, a collapsible bulb 442 is connected tothe lower surface of the end plate 430 by a keep plate 441 to define apump chamber 415. A composite valve 414 provided integrally with amushroom-shaped suction valve and a discharge valve is connected to acenter wall of the pump chamber 415. When the bulb 442 is collapsed ordepressed, fuel vapor or air in the pump chamber 415 pushes open thedischarge valve of the composite valve 414 and flows out into a chamber410, and returns to the fuel tank via a passage not shown. When the bulb442 is released, the pump chamber 415 assumes vacuum pressure uponexpansion of the bulb, and fuel vapor, air and/or some liquid fuel inthe fuel metering chamber 413 lift open the peripheral edge of thecomposite valve 414 via passages 428, 429 and 440 and is drawn into thepump chamber 415.

[0117] As shown in FIG. 41, the peripheral edge of the lid plate 434 isreinforced by ribs 434 b and connected to the carburetor body 438 by apair of bolts 450. The lid plate 434 has a boss portion 432 thatthreadedly receives an idling adjusting bolt 451. The idling adjustingbolt 451 controls a return position or an idling position of thethrottle valve lever 421 caused by the force of the coil spring 402(FIG. 40).

[0118] A cam surface on the lower side of the throttle valve lever 421,a ball 452 supported on the lid plate 434 and the coil spring 402 forbiasing and engaging the cam surface with the ball 452 constitute afirst cam mechanism. When the throttle valve lever 421 is rotatedcounterclockwise from an idling position shown in FIG. 41 toward itsposition at wide open throttle, the throttle valve lever 421, thethrottle valve 405 and the needle 416 are lifted up by the engagement ofthe cam surface and the throttle valve lever 421 and the ball 452. Andthe extent to which the throttle hole 405 a is open relative to the airintake passage 417, as well as the extent to which the fuel nozzle 404 ais open, is increased.

[0119] In FIG. 40, there is shown a relation between the throttle hole405 b and the air intake passage 417 which are perpendicular to eachother. However, actually, the idling position of the throttle valvelever 421 is controlled by the adjusting bolt 451, and the throttle hole405 b is disposed obliquely relative to the air intake passage 417.

[0120] In the start fuel increasing mechanism A of the rotary throttlevalve-type carburetor, a start shaft 445 preferably hollow to reduceweight is rotatably supported on a cylindrical portion 434 a as abearing portion formed in the left end of the lid plate 434. A retainingpin 446 projecting from the cylindrical portion 434 a is engaged with agroove 455 formed on the outer peripheral surface of the start shaft445. As shown in FIG. 42, the groove 455 of the start shaft 445 isprovided with spaced apart end walls 455 a and 455 b. The range ofrotation of the start shaft 445 is controlled by the retaining pin 446,and the starting shaft 445 is normally rotated and biased to a firstposition (shown in FIG. 42) by the force of a spring 449. The spring 449(FIG. 41) is wound about the outer peripheral surface of the cylindricalportion 434 a, and one end of the spring 449 is stopped at a start lever445 a of the start shaft 445 and the other end of the spring 449 isstopped at the cylindrical portion 434 a. 1

[0121] A second cam mechanism is provided between the start shaft 445and the throttle valve lever 421, in which an end of the start shaft 445extends below the throttle valve lever 421 as best seen in FIG. 40. Thestart shaft 445 has a flat cam surface 460 a not in contact with thelower surface of the throttle valve lever 421 and a flat cam surface 460b (FIG. 43) in contact with the lower surface of the throttle valvelever 421. The cam surfaces 460 a and 460 b of the start shaft 445 aredisposed at different heights or distances from the center of the startshaft providing cam lifts L1, L2. The cam surface 460 defines at leastpart of an actuator associated with the start shaft.

[0122] In this embodiment, there is provided, at the lower end of thethrottle valve 405, shown in FIG. 40, an air passage 471 whichcommunicates the throttle hole 405 b with the intake passage 417 in thearea of the air passage 471 when the throttle valve 405 is lifted up bythe second cam mechanism. More specifically, in the embodiment shown,the air passage 471 is a split groove 471 a provided in the lower endsurface of the throttle valve 405 generally, adjacent to the opening470. The split groove 471 a extends in a direction crossing the throttlehole 405 b and is wider than the outside diameter of the support 438 c.Preferably, the groove 471 a does not communicate with the air intakepassage until the throttle valve is moved or predetermined distance fromits idle position.

[0123] When a cold engine is going to be started, the start shaft 445 isrotated against the force of the spring 449 until the end wall 455 bimpinges on the retaining pin 446. The cam surface 460 b comes incontact with the lower surface of the throttle valve lever 421 and liftsup the throttle valve lever 421 to increase the opening or flow area ofthe fuel nozzle. Further, the split groove 471 a crosses the air intakepassage 417, and air in the air intake passage 417 upstream of thethrottle valve 405 flows downstream of the air intake passage 417 viathe split groove 471 a to increase the quantity of air delivered fromthe carburetor. In this manner, the cold starting of the engine isfacilitated and a smoother initial engine idling is obtained.

[0124] Ninth Embodiment

[0125] In the embodiment shown in FIGS. 44 and 45, the air passage 471is an inclined bore 471 b, instead of the groove 471 a of the priorembodiment. The bore 471 b is open to the throttle hole 405 b at one endand the outer peripheral surface at the lower end of the throttle valve405 at its other end. The rest of the carburetor may be the same asdiscussed in the prior embodiment with the same reference numbers usedfor similar or identical components.

[0126] In the first position of the start shaft 445, the cam surface 460a of the start shaft 445 extends below the throttle valve lever 421, thepassage 471 b is positioned lower than the air intake passage 417, andonly the throttle hole 405 b is merely communicated with the air intakepassage 417. Normally, the end of the inclined passage 471 b is closedby the inner peripheral surface of the valve chamber 403, but when thethrottle valve lever 421 is lifted up by the second cam mechanism (whenthe start shaft is rotated to its second position), the end of theinclined passage 471 b comes into communication with the air intakepassage 417.

[0127] After the engine has been started, the throttle valve lever 421is rotated toward the fully open throttle position and is disengagedfrom the cam surface 460 b. The start shaft 445 is returned to its firstposition shown in FIG. 40 by the force of the spring 449.

[0128] Tenth Embodiment

[0129] In the embodiment shown in FIGS. 46 to 50, in order to supply arich fuel and air mixture to the engine when the engine is started, astart shaft 532 having a start lever 531 is fitted into a boss portion553 of the lid plate 521. A pin 551 secured to the boss portion 553 isengaged with a groove 550 of the start shaft 532. A spring 533 isinterposed between the start lever 531 and the boss portion 553, and thestart lever 531 is rotated and biased to its first position by the forceof the spring 553. As shown in FIG. 49, a cam 552 on the end portion ofthe start shaft 532 is provided with a flat surface 552 a and a camsurface 552 b, and normally, the flat surface 552 a projects below thethrottle valve lever 522 and is not in contact with the lower surface ofthe throttle valve lever 522. When the start lever 531 is moved to itssecond position, the cam surface 552 b formed on the end of the startshaft 532 comes in contact with the lower surface of the throttle valvelever 522 to lift up the throttle valve lever 522. The cam surface 552 bdefines at least in part an actuator associated with the start shaft.

[0130] As shown in FIGS. 46 to 50, an elongated through hole 554extending in an axial direction of the start shaft 532 is provided onthe lid plate 521 adjacent to a contact point Q (FIG. 49) between thelid plate 521 and the peripheral surface of the start shaft 532.

[0131] In starting the engine, when the start lever 531 and start shaft532 are rotated to their second position (generally in the direction ofthe arrow “x” in FIG. 49) the cam surface 552 b on the end of the startshaft 532 comes in contact with the lower surface of the throttle valvelever 522, as shown in FIG. 50, to lift up the throttle valve. Theneedle 503 suspended from the upper portion of the throttle valve 501moves upward to increase the open area or flow area of the fuel nozzle504 a of the fuel supply pipe 504 to increase the amount of fuelsupplied to the engine.

[0132] When the throttle valve lever 522 is rotated toward its wide openposition (in a direction indicated generally by arrow “y” of FIG. 48)after the engine is warmed-up, the cam surface 552 b on the end of thestart shaft 532 is disengaged from the throttle valve lever 522, and thestart lever 531 is returned to its first position by the force of thespring 533. At this time, as shown in FIG. 50, a corner portion P, wherethe peripheral surface of the start shaft 532 meets the flat surface 552a, passes the through-hole 554, and dust, oil or other contaminates arescraped off the lid plate 521 into the through-hole 554. Accordingly,contaminates are removed from this area so that the returning of thestart shaft 532 from its second position to its first position is notimpaired.

I claim:
 1. A carburetor, comprising: a body having an air intakepassage, and a throttle valve chamber communicated with the air intakepassage; a rotary throttle valve slidably and rotatably received in thethrottle valve chamber between idle and wide open positions to controlthe delivery of a fuel and air mixture to the engine, and having athrough hole to control the flow of air from the carburetor; a fuelnozzle carried by the body and through which fuel flows prior to beingdischarged from the carburetor; a start shaft carried by the carburetorbody for movement between first and second positions; an actuatoroperably associated with the start shaft for movement in response tomovement of the start shaft from its first position to its secondposition to cause movement of the throttle valve in a directionincreasing both the quantity of air flow through the throttle valvethrough hole and the effective flow area of the fuel nozzle compared tothe air flow through the throttle valve through hole and the effectiveflow area of the fuel nozzle when the throttle valve is in an idleposition.
 2. The carburetor of claim 1 wherein the actuator comprises acam that engages and axially moves the throttle valve and a push rodthat rotates the throttle valve when the start shaft is moved to itssecond position.
 3. The carburetor of claim 2 wherein the cam and thepush rod are formed on the start shaft.
 4. The carburetor of claim 1wherein the actuator comprises a cam that engages and axially moves thethrottle valve when the start shaft is moved to its second position. 5.The carburetor of claim 4 wherein the throttle valve defines at least inpart an air passage and the axial movement of the throttle valve causedby the cam communicates the air passage with the air intake passage. 6.The carburetor of claim 5 wherein the air passage is defined at least inpart by a groove in the throttle valve.
 7. The carburetor of claim 5wherein the air passage is defined at least in party by a bore in thethrottle valve.
 8. The carburetor of claim 2 wherein the push rod iscarried by the start shaft.
 9. The carburetor of claim 8 wherein thepush rod is disposed eccentrically relative to the start shaft.
 10. Thecarburetor of claim 8 wherein the start shaft both rotates and movesaxially as it moves between its first and second positions.
 11. Acarburetor, comprising: a body having an air intake passage, and athrottle valve chamber communicated with the air intake passage; arotary throttle valve slidably and rotatably received in the throttlevalve chamber between idle and wide open positions to control thedelivery of a fuel and air mixture to the engine, and having a throughhole to control the flow of air from the carburetor; a fuel nozzlecarried by the body and through which fuel flows prior to beingdischarged from the carburetor; a needle carried by the throttle valvefor reciprocation relative to the fuel nozzle to change the effectiveflow area of the fuel nozzle and thereby control the delivery of fuelfrom the carburetor; a start shaft carried by the carburetor body formovement between first and second positions; a cam operably associatedwith the start shaft and adapted to axially move the throttle valve awayfrom its idle position to move the needle relative to the fuel nozzleand increase the effective flow area of the fuel nozzle permitting anincreased fuel flow through the nozzle; and a push rod associated withthe start shaft for movement relative to the throttle valve when thestart shaft is moved from its first position to its second position torotate the throttle valve away from its idle position to increase theeffective flow area of the hole in the throttle valve and permitincreased air flow therethrough, whereby movement of the start shaftfrom its first position to its second position axially and rotatablydisplaces the throttle valve to change the fuel and air mixturedelivered from the carburetor compared to that delivered from thecarburetor when the throttle valve is in its idle position.
 12. Thecarburetor of claim 11 wherein the push rod and the cam are carried bythe start shaft.
 13. The carburetor of claim 12 wherein the push rod andcam are formed on the start shaft.
 14. The carburetor of claim 12wherein the push rod is threadedly received in the start shaft.
 15. Thecarburetor of claim 12 wherein the push rod is formed at an end of thestart shaft.
 16. The carburetor of claim 2 which also comprises apushing shaft driven for movement by the start shaft as the start shaftmoves between its first and second positions, and wherein the push rodis carried by the pushing shaft.
 17. The carburetor of claim 16 whereinthe start shaft has a projection and the pushing shaft has a groove thatreceives at least a portion of the projection so that movement of thestart shaft causes movement of the pushing shaft due to engagement ofthe projection and groove.
 18. The carburetor of claim 17 wherein thepushing shaft is axially advanced by rotation of the start shaft fromits first position toward its second position.
 19. The carburetor ofclaim 17 wherein the cam is formed on the start shaft.
 20. Thecarburetor of claim 13 wherein the push rod is formed at an end of thestart shaft and the cam is formed on a peripheral surface of the startshaft generally adjacent to the push rod.
 21. The carburetor of claim 12wherein the push rod is spaced from the center of the start shaft. 22.The carburetor of claim 2 which also comprises an arcuate groove formedin the start shaft and a pin carried by the body received in the grooveto cause generally axial movement of the start shaft when the startshaft is rotated.
 23. The carburetor of claim 22 wherein the pin retainsthe start shaft on the body.
 24. The carburetor of claim 2 which alsocomprises a guide tube of the body, a sleeve fitted in the guide tubeand in which at least a portion of the start shaft is received, a grooveformed in the start shaft, and a pin carried by the sleeve and extendingat least in part into the groove to control axial movement of the startshaft as the start shaft is rotated.
 25. The carburetor of claim 24wherein the pin engages the guide tube to prevent rotation of thesleeve.
 26. The carburetor of claim 2 wherein the throttle valve alsohas a throttle valve lever connected to the valve shaft, the throttlevalve lever being driven to drive the throttle valve between its idleand wide open positions, and wherein the cam and push rod engage andmove the throttle valve lever when the start shaft is moved to itssecond position.
 27. The carburetor of claim 2 which also comprises anidling adjusting bolt carried by the body or engagement with thethrottle valve to set the idle position of the throttle valve.
 28. Thecarburetor of claim 2 wherein the push rod engages the throttle valvewhen the throttle valve is in its idle position.
 29. The carburetor ofclaim 2 which also comprises a cam shaft on which the cam is formed, thecam shaft being driven for rotation by the start shaft at least when thestart shaft is rotated from its first position to its second position.30. The carburetor of claim 29 which also comprises a driven gearassociated with the cam shaft and a driving gear associated with thestart shaft for corotation with the start shaft and engaged with thedriven gear to rotate the cam shaft in response to rotation of the startshaft.
 31. The carburetor of claim 30 wherein the driven gear is formedon the cam shaft and the driving gear is formed on the start shaft. 32.The carburetor of claim 30 which also comprises a groove formed in thestart shaft, and a pin carried by the body and received at least in partin the groove so that upon rotation of the start shaft from its firstposition to its second position, the engagement of the groove and thepin causes generally axial movement of the start shaft.
 33. Thecarburetor of claim 32 wherein the push rod is carried by the startshaft.
 34. The carburetor of clam 29 wherein the cam shaft iseccentrically disposed relative to the start shaft.
 35. The carburetorof claim 2 wherein the cam is formed on the push rod.
 36. The carburetorof claim 35 wherein the push rod is carried by the start shaft and isdisposed eccentrically of the start shaft.
 37. The carburetor of claim 2wherein the body has a lid plate through which a portion of the throttlevalve extends and adjacent to which the start shaft is carried, andwherein the lid plate has a hole formed in it closely adjacent to thestart shaft so that contaminants in the area of the start shaft arecommunicated with the hole during at least a portion of the movement ofthe start shaft between its first and second positions.
 38. Thecarburetor of claim 37 wherein the cam is formed on the start shaft anda corner portion is defined between the cam and the adjacent peripheralsurface of the start shaft, the corner portion passing the hole in thelid plate during at least a portion of the movement of the start shaftbetween its first and second positions.
 39. A carburetor, comprising: abody having an air intake passage, and a throttle valve chambercommunicated with the air intake passage; a rotary throttle valveslidably and rotatably received in the throttle valve chamber betweenidle and wide open positions to control the delivery of a fuel and airmixture to the engine, and having a valve shaft, a hole through thevalve shaft to control the flow of air from the carburetor, and an airpassage formed at least in part in the valve shaft that is incommunication with the air intake passage during at least a portion ofthe throttle valve movement away from its idle position; a fuel nozzlecarried by the body and through which fuel flows prior to beingdischarged from the carburetor; a needle carried by the throttle valvefor reciprocation relative to the fuel nozzle to change the effectiveflow area of the fuel nozzle and thereby control the delivery of fuelfrom the carburetor; a start shaft carried by the carburetor body formovement between first and second positions; and a cam operablyassociated with the start shaft and adapted to axially move the throttlevalve away from its idle position to move the needle relative to thefuel nozzle and increase the effective flow area of the fuel nozzlepermitting an increased fuel flow through the nozzle whereby themovement of the throttle valve when the start shaft is rotated to itssecond position communicates the air passage of the throttle valve withthe air intake passage to permit increased air flow through thecarburetor.
 40. The carburetor of claim 39 wherein the air passage isdefined at least in part by a groove formed in the valve shaft.
 41. Thecarburetor of claim 40 wherein the groove is formed at least in part inthe bottom of the valve shaft.
 42. The carburetor of claim 40 whereinthe groove is a split-groove formed at the lower end of the throttlevalve.
 43. The carburetor of claim 40 wherein the groove is disposed sothat it does not communicate with the air intake passage when thethrottle valve is in its idle position, and the groove communicates withthe air intake position when the throttle valve is moved a predetermineddistance from its idle position.
 44. The carburetor of claim 39 whereinthe air passage is defined by a bore formed in the valve shaft.
 45. Thecarburetor of claim 44 wherein the bore communicates at one end with thehole in the throttle valve shaft and at its other end with theperipheral surface of the valve shaft.
 46. The carburetor of claim 44wherein the bore is disposed so that it does not communicate with theair intake passage when the throttle valve is in its idle position, andthe bore communicates with the air intake position when the throttlevalve is moved a predetermined distance from its idle position.
 47. Acarburetor, comprising: a body having an air intake passage, a throttlevalve chamber communicated with the air intake passage, and an opening;a rotary throttle valve slidably and rotatably received in the throttlevalve chamber between idle and wide open positions to control thedelivery of a fuel and air mixture to the engine, and having a valveshaft, and a hole through the valve shaft to control the flow of airfrom the carburetor, a fuel nozzle carried by the body and through whichfuel flows prior to being discharged from the carburetor; a needlecarried by the throttle valve for reciprocation relative to the fuelnozzle to change the effective flow area of the fuel nozzle and therebycontrol the delivery of fuel from the carburetor; a start shaft carriedby the body adjacent at least in part to the opening and moveablebetween first and second positions, the movement of the start shaftcausing at least a portion of the start shaft to pass near the openingto communicate contaminants in the area of the start shaft with theopening; and a cam operably associated with the start shaft and adaptedto axially move the throttle valve away from its idle position to movethe needle relative to the fuel nozzle and increase the effective flowarea of the fuel nozzle permitting an increased fuel flow through thenozzle.
 48. The carburetor of claim 47 wherein the body has a lid platethrough which a portion of the throttle valve extends and adjacent towhich the start shaft is carried, and wherein the opening is formed inthe lid plate.
 49. The carburetor of claim 47 wherein the cam is formedon the start shaft and a corner portion is defined between the cam andthe adjacent peripheral surface of the start shaft, the corner portionpassing the hole in the body during at least a portion of the movementof the start shaft between its first and second positions.
 50. Thecarburetor of claim 49 wherein the body has a lid plate through which aportion of the throttle valve extends and adjacent to which the startshaft is carried, and wherein the opening is formed in the lid plate.